Variable resistance



July 21, 1925. 1,547,143

F. B. cox

VARIABLE RESISTANCE Filed July 9- 1924 2 Shoots-Shoot 1 hum/Tm.-

FQANK x I July 21, 1925. 1,547,143

F. a. cox

VARIABLE RESI STANCE Filed July 9-1924 2 Shun-Shed 2 FRANK 5. Co!

I Wald/rm I w Patented July 21, 1925.

UNITED STATES FRANK BRIMSON COX, 0F LIVERPOOL, ENGLAND.

VARIABLE RESISTANCE.

Application filed July 9, 1924.

To all whom it may concern:

Be it known that I, FRANK BRIMSON Cox, a subject of the King of GreatBritain, residing at Liverpool, in the county of Lancaster, England,have invented certain new and useful Improvements Relating to VariableResistances, of which the following is a specification.

This invention relates to variable electric resistances and controlswitches therefor, and is specially applicable to switchgear forelectric motors.

According to the present invention the resistance comprises several unitresistances usually of differing magnitudes arranged in parallel, and acontrol switch in the circuit of each resistance, the magnitude of the.resistance as a whole being varied by varying the combinations ofindividual resistances in parallel, whereby, with a comparatively smallnumber of individual resistances, a comparatively large number ofcombinations of resistances may be obtained by selective action of theswitches controlling the respective resistances; for example, with fourseparate resistances of differing magnitudes, each controlled by its owncontrol switch in such manner that any desired combination of these,singly or in parallel groups may be obtained, I am able, by selectiveaction of the control switches, to obtain fifteen values of theresistance as a whole, varying fr m a minimum value when all theresistances are in parallel, through intermediate values to a maximumvalue when the highest resistance alone is in circuit.

In carrying out the invention a. number n of resistances of unequalmagnitude are adapted by switch connections and common operating meanstherefor to be introduced into a circuit in such manner that theresistance so introduced may be varied in a number of steps up to 21steps from a maximum value equal to that of the great est resistance toa minimum value equal to that of all the resistances connected inparallel.

I have illustrated my invention in the accompanying drawings, which aremainly of a diagrammatic character, and in which the invention is shownas applied for the pur pose of varying the resistance in series with thearmature of an electric motor, the several modifications illustratingthe various Serial No. 725,092.

ways in which the desired combinations of switches can be operated insuccession.

Figs. 1 and 2 show the arrangement when the switches are closed bymechanical means;

Figs. 3 and 4 show the arrangement when the switches are closed byelectro-magnetic means.

Figs. 5, 6 and 7 show the arrangement when the switches are closed bypneumatic means electrically controlled.

Referring first to Fig. 1:

R R R R and R are resistances of unequal magnitude; one end of each isconnected to the conductor 1, and the other ends are connected torespective contacts 2; the contacts 2 are adapted to be connected to acommon contact 3 by selecting switches S S the common contact 3 isconnected by a conductor 4 to the terminal m of a motor M, the otherterminal m of which is connected to a conductor 5; the respectiveconductors 4 and 5 being adapted to be connected by a circuit breaker Bto the positive and negative supply mains P and N.

m is the shunt winding of the motor.

Each selecting switch S is carried by an arm 6, and the arms are mountedon a com mon spindle 7; and in the case of each switch an arm 8connected to the arm 6 carries a cam roller 9. The cam roller 9 isadapted to be operated by respective. sets of cams C C 0 C and C mountedon an operating shaft D and adapted to be rotated by a handle (Z Eachswitch is provided with a spring 10, which tends normally to open it,and the respective cams tend to close the switches in opposition to thesprings.

The action is as follows Vith the five resistances shown 31 differentresistance magnitudes may be inter posed in the circuit, by thecombinations obtained by closing the individual switches, or by closingall the switches, or by closing various combinations of 2, 3, 4 of theswitches; the resistance interposed in the circuit varying in 31 stepsfrom the maximum value equal to that of the highest individualresistance when its switch only is closed, to a minimum value, when allthe switches are closed, equal to that of all the resistances whenconnected in parallel. Usually it is not necessary to have as many as 31steps, but it will be seen that a number of combinations considerablygreater than the number of resistances employed may be obtained.

In Figs. 3 and 4 the arrangement is substantially similar to thatdescribed except that four resistances R to B only have switchesattached to them, a resistance T being permanently connected across thecircuit, and one of the switches S beingemployed to short circuit allthe resistances through a short circuiting bar P.

In this arrangement the arms 8 of the switches, instead of beingoperated by cams and cam rollers, are operated by electromagnets E E E EE the plungers e of the solenoids being connected to the respective arms8; the solenoids are energized by contacts f carried on respective discsF F F and F or on a common drum carried on the shaft- D adapted to beoperated by the handle (P; the windings of the solenoids are connectedat one end by a wire 11 to one pole of a source of electric supply, andthe other ends are respectively connected to a series of brushes f f f 7and i which brushes make contact with the groups of contacts fieach ofthe latter being connected to the other pole of the said supply.

It will be seen that by rotating the shaft (Z various combinations ofthe switches can be closed whereby the individual resistances R R orvarious combinations of them in parallel are connected in the circuit;fifteen such combinations being possible with the four resistances.

' The, resistance T is introduced so as to provide a steadying efiect,and the short circuiting conductor P is employed to connect the motordirectly across the mains in the pistons 9 0f the pneumatic cylinders Gto G and the action of each pneumatic piston is controlled by valves 9adapted to connect the under side of the piston to, say, a vacuumthrough the pipe 13, or to the atmosphere through the pipes 14:. The

valves are provided with arms 9 which are connected to the plungers e ofaseries of electro magnets E to E the energizing current of theelectromagnets being controlled in the manner described in connectionwith Figs. 3 and at, that is to say by brushes f to f making contactwith contacts f mounted on discs F to F carried by a shaft D operated bya handle d In the drawings I have shown the invention as applied to avariable electric resistance for starting an electric motor; it is to beunderstood however that the invention is applicable generally tovariable resistance devices employed for any purpose.

Having now fully described my invention I declare that what I claim anddesire to secure by LettersPatent is 1. A rheostat comprising, incombination, a plurality of resistances of different magnitudes havingone end of each permanently connected together and to one terminal ofthe circuit to be controlled, an individual switch for connecting theother end of each resistance to the other terminal of the circuit to becontrolled, electromagnetic means for actuating said switches, andmanually controlled means including a rotary commutator for selectivelyenergizing sai'd electromagnetic means to cause the operation of saidswitches in predetermined groups.

2. A. rheostat comprising, in combination, a plurality of resistances ofdifferent magnitudes having one end of each permanently connectedtogether and to one terminal of the circuit to be controlled, anindividual switch for connecting the other end of each resistance to theother terminal of the circuit to be controlled, pneumatic means foractuating said switches, electromagnetic means for controlling saidpneumatic means, and manually operated means including a rotarycommutator for selectively energizing said electromagnetic means tocause the actuation of said switches by said pneumatic means, inpredetermined groups.

In witness whereof I have hereunto set my hand in presence of twosubscribing witnesses. V

FRANK BRIMSON COX. Witnesses: JosErH E. Hmsr, MARGUERITA J ONES.

